1. Field of the Invention
The present invention relates to solar cells and, particularly, to a carbon nanotube based solar cell.
2. Discussion of Related Art
Solar cells can be classified as source materials such as silicon-based (single crystal, poly-crystalline and amorphous) solar cells and compound semiconductor-based solar cells. Among others, solar cells using single crystal silicon substrates are most widely fabricated by virtue of their excellent efficiency in energy conversion and low production cost.
Referring to FIG. 4, the solar cell 30 includes a back electrode 32, a silicon substrate 34, a doped silicon layer 36 and an upper electrode 38 according to the prior art. The back electrode 32 is located on and electrically connected to a lower surface 340 of the silicon substrate 34. A number of cavities 342 are defined in an upper surface 344 of the silicon substrate 34. The doped silicon layer 36 is located on an inside surface 346 of the cavities 342. The upper electrode 38 is located on the upper surface 344 of the silicon substrate 34. The upper electrode 38 includes a conductive metal grid used to increase the transmission of sunlight. However, since the conductive metal isn't transparent, transparent indium tin oxide (ITO) is selected to form the upper electrode 38. Furthermore, the indium tin oxide isn't mechanically and chemically durable, and the distribution of the resistance isn't uniform. As a result, the durability and the photoelectric conversion efficiency are relatively low.
What is needed, therefore, is to provide a solar cell with high photoelectric conversion efficiency and durability, in addition to a uniform distribution of resistance.